<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    
</body>
</html>
<script>
    var a=Number(prompt("请输入年份"))
    if(a%4==0&&a%100!=0||a%400==0){
        alert("是闰年")
    }else{
        alert("不是闰年")
    }
</script>